M57
The famously named "Ring Nebula" is located in the northern constellation of Lyra, and also catalogued as NGC 6720. It is one of the most prominent examples of the deep-sky objects called planetary nebulae (singular, planetary nebula), often abbreviated by astronomers as simply planetaries or PN.
M57 is located in Lyra, south of its brightest star Vega. Vega is the northeastern vertex of the three stars of the Summer Triangle. M57 lies about 40% of the angular distance from β Lyrae to γ Lyra. M57 is best seen through at least a 20 cm (8-inch) telescope, but even a 7.5 cm (3-inch) telescope will show the ring. Larger instruments will show a few darker zones on the eastern and western edges of the ring, and some faint nebulosity inside the disk.
This nebula was discovered by Antoine Darquier de Pellepoix in January, 1779, who reported that it was "...as large as Jupiter and resembles a planet which is fading." Later the same month, Charles Messier independently found the same nebula while searching for comets. It was then entered into his catalogue as the 57th object. Messier and William Herschel also speculated that the nebula was formed by multiple faint stars that were unable to resolve with his telescope. In 1800, Count Friedrich von Hahn discovered the faint central star in the heart of the nebula. In 1864, William Huggins examined the spectra of multiple nebulae, discovering that some of these objects, including M57, displayed the spectra of bright emission lines characteristic of fluorescing glowing gases. Huggins concluded that most planetary nebulae were not composed of unresolved stars, as had been previously suspected, but were nebulosities. 


Recording in H-Alpha, Green and Blue

In physics and astronomy, H-alpha, also written Hα, is a specific red visible spectral line created by hydrogen with a wavelength of 6562.8 Å.


Recording in H-Alpha

In physics and astronomy, H-alpha, also written Hα, is a specific red visible spectral line created by hydrogen with a wavelength of 6562.8 Å.

According to the Bohr model of the atom, electrons exist in quantized energy levels surrounding the atom's nucleus. These energy levels are described by the principal quantum number n = 1, 2, 3, ... . Electrons may only exist in these states, and may only transit between these states.

The set of transitions from n ≥ 3 to n = 2 is called the Balmer series and its members are named sequentially by Greek letters:

  • n = 3 to n = 2 is called Balmer-alpha or H-alpha,
  • n = 4 to n = 2 is called H-beta,
  • n = 5 to n = 2 is called H-gamma, etc.

For the Lyman series the naming convention is:

  • n = 2 to n = 1 is called Lyman-alpha,
  • n = 3 to n = 1 is called Lyman-beta, etc.

H-alpha has a wavelength of 6562.81 Å, is visible in the red part of the electromagnetic spectrum, and is the easiest way for astronomers to trace the ionized hydrogen content of gas clouds. Since it takes nearly as much energy to excite the hydrogenatom's electron from n = 1 to n = 3 as it does to ionize the hydrogen atom, the probability of the electron being excited to n = 3 without being removed from the atom is very small. Instead, after being ionized, the electron and proton recombine to form a new hydrogen atom. In the new atom, the electron may begin in any energy level, and subsequently cascades to the ground state (n = 1), emitting photons with each transition. Approximately half the time, this cascade will include the n = 3 to n = 2 transition and the atom will emit H-alpha light. Therefore, the H-alpha line occurs where hydrogen is being ionized.

The H-alpha line saturates (self-absorbs) relatively easily because hydrogen is the primary component of nebulae, so while it can indicate the shape and extent of the cloud, it cannot be used to accurately determine the cloud's mass. Instead, molecules such as carbon dioxide, carbon monoxide, formaldehyde, ammonia, or methyl cyanide are typically used to determine the mass of a cloud.




LRGB Combination 300 seconds